In Vitro Antimicrobial Screening of 27 Extracts from 21 Medicinal Plant Species Against Selected Clinically Relevant Bacterial and Fungal Pathogens

Abstract

Background: Antimicrobial resistance (AMR) has emerged as a major global public health challenge because of its increasing prevalence, which is largely driven by the inappropriate and excessive use of antibiotics. This problem has renewed scientific interest in medicinal plants, which are a rich source of bioactive metabolites and have been used for centuries in traditional medicine to treat infectious diseases. Objectives: To evaluate and compare the antimicrobial activities of ethanol extracts of different organs of selected medicinal plants against reference microorganisms and clinically isolated bacterial and fungal pathogens. Methods: Ethanol extracts of different parts of 21 medicinal plants belonging to several botanical families were tested using the broth microdilution method. Antimicrobial activity was assessed by determining the minimum inhibitory concentration (MIC) values against the quality control strains and the corresponding clinical isolates. Results: The tested extracts exhibited antimicrobial activity, with MIC values ranging from 8 to > 128 µg/mL against quality control strains of Escherichia coli, Klebsiella pneumoniae, Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, Candida albicans, Candida krusei, and their isolated strains. Among the tested samples, the flower extract of Alcea biennis showed the strongest antibacterial activity, with MIC values of 8 µg/mL against the quality control strains of E. coli, B. subtilis, and E. faecalis and 16 µg/mL against the clinical strains. The herb extract of Cistus creticus also showed strong antibacterial activity against the reference strains of E. coli and S. aureus, whereas the herb extract of Lamium purpureum inhibited the quality control strain of S. aureus, with an MIC value of 8 µg/mL. Conclusions: Among the investigated medicinal plants, A. biennis and C. creticus exhibited notable antimicrobial activity. These results support further phytochemical characterization and pharmacological evaluation of these species as promising sources of novel antimicrobial compounds.